Research On Tectonic Characteristics In Quaternary Of The Dao Jie Basin In Nu Jiang Fault Zone

A series of tectonic basins in Cenozoic were developed in the south of Nujiang fault zone (the south of Liu Ku), distributed with beads in line. As the biggest and the most developed faulted basin in quaternary strata, Daojie basin is the most perfect area for researching on tectonic activity in Quaternary of Nujiang fault zone. It is a graben faulted basin developed when blocks in the western Yunnan undergone otherness movement under the background of overall oblique uplift. East branch of Nujiang fault control the physiognomy of the basin, and its main sediments are diluvium, which are derived from Gaoligong Mountain and located in the west of Nujiang River.Nujiang fault is a large inner continental strike-slip fault in eastern Tibetan margin. It is closely related to uplift of the Tibetan plateau. Based on study object of the Daojie basin, clue of strata in Quaternary and basin-controlled faults, the thesis research on tectonic activity of the basin, which reflect tectonic activity of Nujiang fault since Quaternary. It helps to understand the tectonic activity characteristic of Nujiang fault, which is important for revealing mechanism of the eastern extrusion of Tibetan plateau and discussing anti-seismic of hydropower engineering in Nujiang River area. The main achievements and new understandings are described as follows:1. Through drilling, finding strata profile, measuring transverse section of the basin, the filling sequence in Quaternary and time sequence are established. Analysis of the filling sequence indicates there may be four tectonic activity periods after formation of the basin, which are proved in fault activity and tectonic geomorphology. The first three tectonic activity periods are caused by Nujiang fault, and the fourth is the fault activity in Daojie basin.2. Combined with OSL/TL dating and strata data, analysis of pollen show climate change was not stable since late middle Pleistocene, namely, the characteristic of alternating warm wet and cool dry fluctuation change. 3. Using Post-operation difference GPS, it surveyed 8 vertical sections of gully in the west of Daojie basin. It is found that the formation of gully rapids and pediments were related to basin-controlled fault from the relations between vertical sections of gully and pediments. Besides, it is inferred that there should be a fault in the edge of Daojie basin through the relationship of vertical section, pediment and basin-controlled fault.4. Using Post-operation difference GPS, it measured several data of Nujiang River terraces, and taken many OSL samples to data. Through calculating, it show that the average rate of uplift in western Yunnan is 1.17mm/a since late Pleistocene.5. Analysis of the data about strata, tectonic geomorphology and fault activity indicate that newest activity of the south of Nujiang fault is early-middle Pleistocene, namely, there is no obvious signs of activity since late Quaternary. Some sub-faults in basins which developed along Nujiang fault are still active since late Pleistocene, and are still smaller.6. Western Yunnan undergone overall oblique uplift since the Quaternary, following different lift of blocks. Modern tectonic stress field in western Yunnan is characteristic of NE-direction compression and SW-direction extension. Under this tectonic background, Nujiang fault is characteristic of tensile-shear activity, and control the development of Daojie basin through 3 tectonic activity periods.